drm/i915/gvt: Fix firmware loading interface for GVT-g golden HW state

Firmware loading interface for GVT-g golden HW state has been broken
before. This patch fixes GVT-g firmware loading interface. A user should
apply this patch if he wants to load GVT-g golden HW state from firmware
interface.

Fixes: 579cea5f

 ("drm/i915/gvt: golden virtual HW state management")
Cc: Zhenyu Wang <zhenyuw@linux.intel.com>
Cc: drm-intel-fixes@lists.freedesktop.org
Signed-off-by: Zhi Wang <zhi.a.wang@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>